Add stage-c and stage-b autocomplete models (Q8_0 GGUF)

stage-c (default): Qwen2.5-Coder-0.5B fine-tuned for suffix-first FIM with
repo/symbol-context headers. stage-b: same without context headers.
manifest.json lists files, SHA-256s, prompt profiles and the pinned llama.cpp
build for the Local Autocomplete extension's managed mode.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

NOTICE

@@ -0,0 +1,7 @@
+These model files are modified versions of Qwen2.5-Coder-0.5B (https://huggingface.co/Qwen/Qwen2.5-Coder-0.5B),
+Copyright (c) Alibaba Cloud, licensed under the Apache License, Version 2.0 (see LICENSE).
+
+Modifications: full-parameter fine-tuning for suffix-first fill-in-the-middle completion
+(and, for stage-c, a repository/symbol-context header), followed by Q8_0 GGUF conversion.
+Fine-tuning data: permissively licensed (MIT) open-source TypeScript/Vue repositories and
+the publisher's own code. Secrets were scrubbed from the training data.